The low-resolution display panels such as Vacuum Fluorescent Display, Light-Emitting Diode, Liquid Crystal Display and others are often used for visual representation of numeric data. The goal of current invention was to use the low-resolution displays for visual representation of gray-scaled video and audio signals. The main problem was how to reconcile the two-value states for each pixel on the low-resolution display (only ‘on’ or ‘off’) with requirements to represent the multiple-value gray-scaled data from video sources.
The current invention uses the so-called Pulse Density Modulation to represent gray-scaled video data on the low-resolution display. The property of Pulse Density Modulation is that it conveys the data values by asserting the variable number of pulses in each fixed period of time. This characteristic of Pulse Density Modulation is suitable to transmit the brightness value of each pixel due to the property of human eye to integrate binary (only ‘on’ or ‘off’) brightness pulses over the time to perceive them as the gray-scaled pixels.
The two-dimensional spatial Pulse Density Modulation was used in the prior art for halftoning image rendering systems for printing color and gray-scaled documents. The current invention uses temporal Pulse Density Modulation technique to represent changing-in-time signals.